Intradermal injections are used for delivering a variety of diagnostic and treatment compositions into a patient. Intradermal injections are typically injections of a relatively small amount of medicament into the dermis or dermal layer or even into a lower portion of the epidermis (FIG. 2A) of a patient's skin. Substances may be injected intradermally for diagnostic testing, such as to determine a patient's immunity status against tuberculosis and the status of allergic diseases. Vaccines, drugs and other compounds may also be delivered intradermally. In many instances, intradermal delivery is preferred because it generally requires a smaller volume dose of the diagnostic or treatment compound than other delivery techniques. There is considerable variation in the thickness of a patient's skin, both between individuals and within the same individual at different sites of the body. Generally the outer skin layer, or the epidermis, typically has a thickness between two hundred and five hundred microns (200-500 μm) and the dermis, the inner and thicker layer of the skin, generally has a thickness between one and one-half to three and one-half millimeters (1.5-3.5 mm).
Making intradermal injections is difficult and generally requires an experienced nurse or medical professional. Incorrect placement of the tip of the cannula may lead to a failed injection. The placement of the cannula tip deeper than about three millimeters (3.0 mm) has the potential of delivering the injection into the subcutaneous region, where the intradermal dosage may be insufficient. Incorrect placement of the cannula may also puncture the skin again after being inserted into dermis, with the delivered compound being lost on the surface of the skin. Injection is often followed by a jet effect, with the compound exiting the injection site through the puncture track. The jet effect is even more pronounced for injections through a cannula placed perpendicular to the injection site and in particular for shallow delivery. The success of intradermal injections is often determined by the skill and experience of the individual healthcare professional administering the injection. The preferred intradermal injection technique (using a standard cannula), requires the healthcare professional to stretch the skin, orient the cannula bevel to face upward, and insert a short bevel cannula at an angle of around ten to fifteen degrees (10-15°) relative to a surface of the skin, while also assuring that two to three millimeters (2-3 mm) of the cannula are located in the skin. The cannula tip ideally ends up positioned in the dermis or close to the dermis/epidermis boundary. The compound is slowly injected into the skin of the patient, forming a blister or wheal. The insertion of the cannula at an incorrect angle and/or depth results in a failed intradermal injection, which is typically repeated, causing additional pain and discomfort as well as ineffective treatment to the patient. Intradermal (ID) injection has been considered for immunization in the past, but has generally been rejected in favor of more reliable intramuscular or subcutaneous routes of administration because of the difficulty in making a successful ID injections, particularly when the injections are administered by relatively unskilled healthcare professionals.
Administration into the region of the intradermal space has been routinely used in the Mantoux tuberculin test, in which a purified protein derivative is injected at a shallow angle to the skin surface using a twenty-seven (27) or thirty (30) gauge cannula and a standard syringe. The technique is known to be quite difficult to perform and generally requires specialized training. A degree of imprecision in the placement of the injection results in a significant number of false negative test results. As a result, the Mantoux approach has not led to the use of intradermal injection for systemic administration of substances, despite the advantage of requiring smaller doses of substances, because the absorption of the medicament into the dermal skin layer is typically superior to injection of the same substance using alternative techniques.
It would be desirable to design and manufacture an intradermal injection adapter that provides a relatively simple, reliable intradermal injection, is relatively easy to use, is relatively cost effective to the user and limits waste of medicament. The cannula of the intradermal injection adapter is preferably statically mounted to or fixed relative to a body of the adapter and/or a barrel of a syringe or pen in an assembled configuration.